As an example of a switch array capable of selectively making and breaking any connection of a plurality of input lines and a plurality of output lines, Japanese unexamined patent publication No. 10-283893 discloses a relay-embedded board. This relay-embedded board disclosed in publication No. 10-283893 includes nine ultra small relays embedded on a thin substrate, each relay being placed in each cross area where three inputs and three outputs cross each other. This example allows any desired relays to be switched on and off.
Because the relays of the relay-embedded board disclosed in publication No. 10-283893 are ultra small, the contact capacity of each relay is also small. The relay-embedded board can pass and interrupt a minute amount of control current, but can not be used for some applications such as lighting apparatuses, because switching on and off such lighting apparatuses requires the relays to pass and interrupt a few amperes of current.
One possibility to allow the flow of such a large current is to use a large relay, however, such a large relay requires a relatively large installation space. Especially, when the large relay is used for a switch array having many cross areas, for example an array size of 128×128 or 256×256, the apparatus incorporating the switch array will be extremely large. Further, if an on-resistance at a relay contact cannot be maintained at 1Ω or lower, the relay causes voltage drop at the relay contact or produces heat at the relay contact when a large current passes through the relay in the on state. Besides, in order to maintain the on state, a driving current must be kept flowing through a relay's coil which is closed in the on state, therefore increasing a consumption current.
There are switch arrays using switching elements such as a MOSFET instead of the relay contact. However, such switch arrays have a high on-resistance and cause a large amount of current leakage in the off state, whereby being prone to break the elements during the flow of the large current.